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authorYiannis Tsiouris <[email protected]>2014-01-28 18:16:54 +0200
committerYiannis Tsiouris <[email protected]>2014-03-07 18:35:03 +0200
commit030fd3f190a44bef059e7490c4b9c615088287d8 (patch)
tree251e9cfbd442f33b37379e879862646430ec3a37 /lib/hipe/llvm/hipe_llvm_main.erl
parent7a490d5cff3f033901ab6cac6c0fc1fd7bcb22c7 (diff)
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Implement the LLVM backend
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+%% -*- erlang-indent-level: 2 -*-
+-module(hipe_llvm_main).
+
+-export([rtl_to_native/4]).
+
+-include("../../kernel/src/hipe_ext_format.hrl").
+-include("hipe_llvm_arch.hrl").
+-include("elf_format.hrl").
+
+%% @doc Translation of RTL to a loadable object. This function takes the RTL
+%% code and calls hipe_rtl_to_llvm:translate/2 to translate the RTL code to
+%% LLVM code. After this, LLVM asm is printed to a file and the LLVM tool
+%% chain is invoked in order to produce an object file.
+rtl_to_native(MFA, RTL, Roots, Options) ->
+ %% Compile to LLVM and get Instruction List (along with infos)
+ {LLVMCode, RelocsDict, ConstTab} =
+ hipe_rtl_to_llvm:translate(RTL, Roots),
+ %% Fix function name to an acceptable LLVM identifier (needed for closures)
+ {_Module, Fun, Arity} = hipe_rtl_to_llvm:fix_mfa_name(MFA),
+ %% Write LLVM Assembly to intermediate file (on disk)
+ {ok, Dir, ObjectFile} =
+ compile_with_llvm(Fun, Arity, LLVMCode, Options, false),
+ %%
+ %% Extract information from object file
+ %%
+ ObjBin = open_object_file(ObjectFile),
+ %% Read and set the ELF class
+ elf_format:set_architecture_flag(ObjBin),
+ %% Get labels info (for switches and jump tables)
+ Labels = elf_format:get_rodata_relocs(ObjBin),
+ {Switches, Closures} = get_tables(ObjBin),
+ %% Associate Labels with Switches and Closures with stack args
+ {SwitchInfos, ExposedClosures} =
+ correlate_labels(Switches ++ Closures, Labels),
+ %% SwitchInfos: [{"table_50", [Labels]}]
+ %% ExposedClosures: [{"table_closures", [Labels]}]
+
+ %% Labelmap contains the offsets of the labels in the code that are
+ %% used for switch's jump tables
+ LabelMap = create_labelmap(MFA, SwitchInfos, RelocsDict),
+ %% Get relocation info
+ TextRelocs = elf_format:get_text_relocs(ObjBin),
+ %% AccRefs contains the offsets of all references to relocatable symbols in
+ %% the code:
+ AccRefs = fix_relocations(TextRelocs, RelocsDict, MFA),
+ %% Get stack descriptors
+ SDescs = get_sdescs(ObjBin),
+ %% FixedSDescs are the stack descriptors after correcting calls that have
+ %% arguments in the stack
+ FixedSDescs =
+ fix_stack_descriptors(RelocsDict, AccRefs, SDescs, ExposedClosures),
+ Refs = AccRefs ++ FixedSDescs,
+ %% Get binary code from object file
+ BinCode = elf_format:extract_text(ObjBin),
+ %% Remove temp files (if needed)
+ ok = remove_temp_folder(Dir, Options),
+ %% Return the code together with information that will be used in the
+ %% hipe_llvm_merge module to produce the final binary that will be loaded
+ %% by the hipe unified loader.
+ {MFA, BinCode, byte_size(BinCode), ConstTab, Refs, LabelMap}.
+
+%%------------------------------------------------------------------------------
+%% LLVM tool chain
+%%------------------------------------------------------------------------------
+
+%% @doc Compile function FunName/Arity to LLVM. Return Dir (in order to remove
+%% it if we do not want to store temporary files) and ObjectFile name that
+%% is created by the LLVM tools.
+compile_with_llvm(FunName, Arity, LLVMCode, Options, UseBuffer) ->
+ Filename = atom_to_list(FunName) ++ "_" ++ integer_to_list(Arity),
+ %% Save temp files in a unique folder
+ Dir = unique_folder(FunName, Arity, Options),
+ ok = file:make_dir(Dir),
+ %% Print LLVM assembly to file
+ OpenOpts = [append, raw] ++
+ case UseBuffer of
+ %% true -> [delayed_write]; % Use delayed_write!
+ false -> []
+ end,
+ {ok, File_llvm} = file:open(Dir ++ Filename ++ ".ll", OpenOpts),
+ hipe_llvm:pp_ins_list(File_llvm, LLVMCode),
+ %% delayed_write can cause file:close not to do a close, hence the two calls
+ ok = file:close(File_llvm),
+ __ = file:close(File_llvm),
+ %% Invoke LLVM compiler tools to produce an object file
+ llvm_opt(Dir, Filename, Options),
+ llvm_llc(Dir, Filename, Options),
+ compile(Dir, Filename, "gcc"), %%FIXME: use llc -filetype=obj and skip this!
+ {ok, Dir, Dir ++ Filename ++ ".o"}.
+
+%% @doc Invoke opt tool to optimize the bitcode (_name.ll -> _name.bc).
+llvm_opt(Dir, Filename, Options) ->
+ Source = Dir ++ Filename ++ ".ll",
+ Dest = Dir ++ Filename ++ ".bc",
+ OptLevel = trans_optlev_flag(opt, Options),
+ OptFlags = [OptLevel, "-mem2reg", "-strip"],
+ Command = "opt " ++ fix_opts(OptFlags) ++ " " ++ Source ++ " -o " ++ Dest,
+ %% io:format("OPT: ~s~n", [Command]),
+ case os:cmd(Command) of
+ "" -> ok;
+ Error -> exit({?MODULE, opt, Error})
+ end.
+
+%% @doc Invoke llc tool to compile the bitcode to object file
+%% (_name.bc -> _name.o).
+llvm_llc(Dir, Filename, Options) ->
+ Source = Dir ++ Filename ++ ".bc",
+ OptLevel = trans_optlev_flag(llc, Options),
+ Align = find_stack_alignment(),
+ LlcFlags = [OptLevel, "-code-model=medium", "-stack-alignment=" ++ Align
+ , "-tailcallopt", "-filetype=asm"], %%FIXME
+ Command = "llc " ++ fix_opts(LlcFlags) ++ " " ++ Source,
+ %% io:format("LLC: ~s~n", [Command]),
+ case os:cmd(Command) of
+ "" -> ok;
+ Error -> exit({?MODULE, llc, Error})
+ end.
+
+%% @doc Invoke the compiler tool ("gcc", "llvmc", etc.) to generate an object
+%% file from native assembly.
+compile(Dir, Fun_Name, Compiler) ->
+ Source = Dir ++ Fun_Name ++ ".s",
+ Dest = Dir ++ Fun_Name ++ ".o",
+ Command = Compiler ++ " -c " ++ Source ++ " -o " ++ Dest,
+ %% io:format("~s: ~s~n", [Compiler, Command]),
+ case os:cmd(Command) of
+ "" -> ok;
+ Error -> exit({?MODULE, cc, Error})
+ end.
+
+find_stack_alignment() ->
+ case get(hipe_target_arch) of
+ x86 -> "4";
+ amd64 -> "8";
+ _ -> exit({?MODULE, find_stack_alignment, "Unimplemented architecture"})
+ end.
+
+%% @doc Join options.
+fix_opts(Opts) ->
+ string:join(Opts, " ").
+
+%% @doc Translate optimization-level flag (default is "O2").
+trans_optlev_flag(Tool, Options) ->
+ Flag = case Tool of
+ opt -> llvm_opt;
+ llc -> llvm_llc
+ end,
+ case proplists:get_value(Flag, Options) of
+ o0 -> ""; % "-O0" does not exist in opt tool
+ o1 -> "-O1";
+ o2 -> "-O2";
+ o3 -> "-O3";
+ undefined -> "-O2"
+ end.
+
+%%------------------------------------------------------------------------------
+%% Functions to manage Relocations
+%%------------------------------------------------------------------------------
+
+%% @doc Get switch table and closure table.
+get_tables(Elf) ->
+ %% Search Symbol Table for an entry with name prefixed with "table_":
+ Triples = elf_format:get_tab_entries(Elf),
+ Switches = [T || T={"table_" ++ _, _, _} <- Triples],
+ Closures = [T || T={"table_closures" ++ _, _, _} <- Switches],
+ {Switches, Closures}.
+
+%% @doc This function associates symbols who point to some table of labels with
+%% the corresponding offsets of the labels in the code. These tables can
+%% either be jump tables for switches or a table which contains the labels
+%% of blocks that contain closure calls with more than ?NR_ARG_REGS.
+correlate_labels([], _L) -> {[], []};
+correlate_labels(Tables, Labels) ->
+ %% Sort "Tables" based on "ValueOffsets"
+ OffsetSortedTb = lists:ukeysort(2, Tables),
+ %% Unzip offset-sorted list of "Switches"
+ {Names, _Offsets, TablesSizeList} = lists:unzip3(OffsetSortedTb),
+ %% Associate switch names with labels
+ L = split_list(Labels, TablesSizeList),
+ %% Zip back! (to [{SwitchName, Values}])
+ NamesValues = lists:zip(Names, L),
+ case lists:keytake("table_closures", 1, NamesValues) of
+ false -> %% No closures in the code, no closure table
+ {NamesValues, []};
+ {value, ClosureTableNV, SwitchesNV} ->
+ {SwitchesNV, ClosureTableNV}
+ end.
+
+%% @doc Create a gb_tree which contains information about the labels that used
+%% for switch's jump tables. The keys of the gb_tree are of the form
+%% {MFA, Label} and the values are the actual Offsets.
+create_labelmap(MFA, SwitchInfos, RelocsDict) ->
+ create_labelmap(MFA, SwitchInfos, RelocsDict, gb_trees:empty()).
+
+create_labelmap(_, [], _, LabelMap) -> LabelMap;
+create_labelmap(MFA, [{Name, Offsets} | Rest], RelocsDict, LabelMap) ->
+ case dict:fetch(Name, RelocsDict) of
+ {switch, {_TableType, LabelList, _NrLabels, _SortOrder}, _JTabLab} ->
+ KVDict = lists:ukeysort(1, lists:zip(LabelList, Offsets)),
+ NewLabelMap = insert_to_labelmap(KVDict, LabelMap),
+ create_labelmap(MFA, Rest, RelocsDict, NewLabelMap);
+ _ ->
+ exit({?MODULE, create_labelmap, "Not a jump table!"})
+ end.
+
+%% @doc Insert a list of [{Key,Value}] to a LabelMap (gb_tree).
+insert_to_labelmap([], LabelMap) -> LabelMap;
+insert_to_labelmap([{Key, Value}|Rest], LabelMap) ->
+ case gb_trees:lookup(Key, LabelMap) of
+ none ->
+ insert_to_labelmap(Rest, gb_trees:insert(Key, Value, LabelMap));
+ {value, Value} -> %% Exists with the *exact* same Value.
+ insert_to_labelmap(Rest, LabelMap)
+ end.
+
+%% @doc Correlate object file relocation symbols with info from translation to
+%% llvm code.
+fix_relocations(Relocs, RelocsDict, MFA) ->
+ fix_relocs(Relocs, RelocsDict, MFA, []).
+
+fix_relocs([], _, _, RelocAcc) -> RelocAcc;
+fix_relocs([{Name, Offset}|Rs], RelocsDict, {ModName,_,_}=MFA, RelocAcc) ->
+ case dict:fetch(Name, RelocsDict) of
+ {atom, AtomName} ->
+ fix_relocs(Rs, RelocsDict, MFA,
+ [{?LOAD_ATOM, Offset, AtomName}|RelocAcc]);
+ {constant, Label} ->
+ fix_relocs(Rs, RelocsDict, MFA,
+ [{?LOAD_ADDRESS, Offset, {constant, Label}}|RelocAcc]);
+ {switch, _, JTabLab} -> %% Treat switch exactly as constant
+ fix_relocs(Rs, RelocsDict, MFA,
+ [{?LOAD_ADDRESS, Offset, {constant, JTabLab}}|RelocAcc]);
+ {closure, _}=Closure ->
+ fix_relocs(Rs, RelocsDict, MFA,
+ [{?LOAD_ADDRESS, Offset, Closure}|RelocAcc]);
+ {call, {bif, BifName, _}} ->
+ fix_relocs(Rs, RelocsDict, MFA,
+ [{?CALL_LOCAL, Offset, BifName}|RelocAcc]);
+ %% MFA calls to functions in the same module are of type 3, while all
+ %% other MFA calls are of type 2.
+ {call, {ModName,_F,_A}=CallMFA} ->
+ fix_relocs(Rs, RelocsDict, MFA,
+ [{?CALL_LOCAL, Offset, CallMFA}|RelocAcc]);
+ {call, CallMFA} ->
+ fix_relocs(Rs, RelocsDict, MFA,
+ [{?CALL_REMOTE, Offset, CallMFA}|RelocAcc]);
+ Other ->
+ exit({?MODULE, fix_relocs,
+ {"Relocation not in relocation dictionary", Other}})
+ end.
+
+%%------------------------------------------------------------------------------
+%% Functions to manage Stack Descriptors
+%%------------------------------------------------------------------------------
+
+%% @doc This function takes an ELF Object File binary and returns a proper sdesc
+%% list for Erlang/OTP System's loader. The return value should be of the
+%% form:
+%% {
+%% 4, Safepoint Address,
+%% {ExnLabel OR [], FrameSize, StackArity, {Liveroot stack frame indexes}},
+%% }
+get_sdescs(Elf) ->
+ case elf_format:extract_note(Elf, ?NOTE_ERLGC_NAME) of
+ <<>> -> % Object file has no ".note.gc" section!
+ [];
+ NoteGC_bin ->
+ %% Get safe point addresses (stored in ".rela.note.gc" section):
+ RelaNoteGC = elf_format:extract_rela(Elf, ?NOTE(?NOTE_ERLGC_NAME)),
+ SPCount = length(RelaNoteGC),
+ T = SPCount * ?SP_ADDR_SIZE,
+ %% Pattern match fields of ".note.gc":
+ <<SPCount:(?bits(?SP_COUNT_SIZE))/integer-little, % Sanity check!
+ SPAddrs:T/binary, % NOTE: In 64bit they are relocs!
+ StkFrameSize:(?bits(?SP_STKFRAME_SIZE))/integer-little,
+ StkArity:(?bits(?SP_STKARITY_SIZE))/integer-little,
+ _LiveRootCount:(?bits(?SP_LIVEROOTCNT_SIZE))/integer-little, % Skip
+ Roots/binary>> = NoteGC_bin,
+ LiveRoots = get_liveroots(Roots, []),
+ %% Extract information about the safe point addresses:
+ SPOffs =
+ case elf_format:is64bit() of
+ true -> %% Find offsets in ".rela.note.gc":
+ elf_format:get_rela_addends(RelaNoteGC);
+ false -> %% Find offsets in SPAddrs (in ".note.gc"):
+ get_spoffs(SPAddrs, [])
+ end,
+ %% Extract Exception Handler labels:
+ ExnHandlers = elf_format:get_exn_handlers(Elf),
+ %% Combine ExnHandlers and Safe point addresses (return addresses):
+ ExnAndSPOffs = combine_ras_and_exns(ExnHandlers, SPOffs, []),
+ create_sdesc_list(ExnAndSPOffs, StkFrameSize, StkArity, LiveRoots, [])
+ end.
+
+%% @doc Extracts a bunch of integers (live roots) from a binary. Returns a tuple
+%% as need for stack descriptors.
+get_liveroots(<<>>, Acc) ->
+ list_to_tuple(Acc);
+get_liveroots(<<Root:?bits(?LR_STKINDEX_SIZE)/integer-little,
+ MoreRoots/binary>>, Acc) ->
+ get_liveroots(MoreRoots, [Root | Acc]).
+
+%% @doc Extracts a bunch of integers (safepoint offsets) from a binary. Returns
+%% a tuple as need for stack descriptors.
+get_spoffs(<<>>, Acc) ->
+ lists:reverse(Acc);
+get_spoffs(<<SPOff:?bits(?SP_ADDR_SIZE)/integer-little, More/binary>>, Acc) ->
+ get_spoffs(More, [SPOff | Acc]).
+
+combine_ras_and_exns(_, [], Acc) ->
+ lists:reverse(Acc);
+combine_ras_and_exns(ExnHandlers, [RA | MoreRAs], Acc) ->
+ %% FIXME: do something better than O(n^2) by taking advantage of the property
+ %% ||ExnHandlers|| <= ||RAs||
+ Handler = find_exn_handler(RA, ExnHandlers),
+ combine_ras_and_exns(ExnHandlers, MoreRAs, [{Handler, RA} | Acc]).
+
+find_exn_handler(_, []) ->
+ [];
+find_exn_handler(RA, [{Start, End, Handler} | MoreExnHandlers]) ->
+ case (RA >= Start andalso RA =< End) of
+ true ->
+ Handler;
+ false ->
+ find_exn_handler(RA, MoreExnHandlers)
+ end.
+
+create_sdesc_list([], _, _, _, Acc) ->
+ lists:reverse(Acc);
+create_sdesc_list([{ExnLbl, SPOff} | MoreExnAndSPOffs],
+ StkFrameSize, StkArity, LiveRoots, Acc) ->
+ Hdlr = case ExnLbl of
+ 0 -> [];
+ N -> N
+ end,
+ create_sdesc_list(MoreExnAndSPOffs, StkFrameSize, StkArity, LiveRoots,
+ [{?SDESC, SPOff, {Hdlr, StkFrameSize, StkArity, LiveRoots}}
+ | Acc]).
+
+%% @doc This function is responsible for correcting the stack descriptors of
+%% the calls that are found in the code and have more than NR_ARG_REGS
+%% (thus, some of their arguments are passed to the stack). Because of the
+%% Reserved Call Frame feature that the LLVM uses, the stack descriptors
+%% are not correct since at the point of call the frame size is reduced
+%% proportionally to the number of arguments that are passed on the stack.
+%% Also the offsets of the roots need to be re-adjusted.
+fix_stack_descriptors(_, _, [], _) ->
+ [];
+fix_stack_descriptors(RelocsDict, Relocs, SDescs, ExposedClosures) ->
+ %% NamedCalls are MFA and BIF calls that need fix
+ NamedCalls = calls_with_stack_args(RelocsDict),
+ NamedCallsOffs = calls_offsets_arity(Relocs, NamedCalls),
+ ExposedClosures1 =
+ case dict:is_key("table_closures", RelocsDict) of
+ true -> %% A Table with closures exists
+ {table_closures, ArityList} = dict:fetch("table_closures", RelocsDict),
+ case ExposedClosures of
+ {_, Offsets} ->
+ lists:zip(Offsets, ArityList);
+ _ ->
+ exit({?MODULE, fix_stack_descriptors,
+ {"Wrong exposed closures", ExposedClosures}})
+ end;
+ false ->
+ []
+ end,
+ ClosuresOffs = closures_offsets_arity(ExposedClosures1, SDescs),
+ fix_sdescs(NamedCallsOffs ++ ClosuresOffs, SDescs).
+
+%% @doc This function takes as argument the relocation dictionary as produced by
+%% the translation of RTL code to LLVM and finds the names of the calls
+%% (MFA and BIF calls) that have more than NR_ARG_REGS.
+calls_with_stack_args(Dict) ->
+ calls_with_stack_args(dict:to_list(Dict), []).
+
+calls_with_stack_args([], Calls) -> Calls;
+calls_with_stack_args([ {_Name, {call, {M, F, A}}} | Rest], Calls)
+ when A > ?NR_ARG_REGS ->
+ Call =
+ case M of
+ bif -> {F,A};
+ _ -> {M,F,A}
+ end,
+ calls_with_stack_args(Rest, [Call|Calls]);
+calls_with_stack_args([_|Rest], Calls) ->
+ calls_with_stack_args(Rest, Calls).
+
+%% @doc This function extracts the stack arity and the offset in the code of
+%% the named calls (MFAs, BIFs) that have stack arguments.
+calls_offsets_arity(AccRefs, CallsWithStackArgs) ->
+ calls_offsets_arity(AccRefs, CallsWithStackArgs, []).
+
+calls_offsets_arity([], _, Acc) -> Acc;
+calls_offsets_arity([{Type, Offset, Term} | Rest], CallsWithStackArgs, Acc)
+ when Type =:= ?CALL_REMOTE orelse Type =:= ?CALL_LOCAL ->
+ case lists:member(Term, CallsWithStackArgs) of
+ true ->
+ Arity =
+ case Term of
+ {_M, _F, A} -> A;
+ {_F, A} -> A
+ end,
+ calls_offsets_arity(Rest, CallsWithStackArgs,
+ [{Offset + 4, Arity - ?NR_ARG_REGS} | Acc]);
+ false ->
+ calls_offsets_arity(Rest, CallsWithStackArgs, Acc)
+ end;
+calls_offsets_arity([_|Rest], CallsWithStackArgs, Acc) ->
+ calls_offsets_arity(Rest, CallsWithStackArgs, Acc).
+
+%% @doc This function extracts the stack arity and the offsets of closures that
+%% have stack arity. The Closures argument represents the
+%% hipe_bifs:llvm_exposure_closure/0 calls in the code. The actual closure
+%% is the next call in the code, so the offset of the next call must be
+%% calculated from the stack descriptors.
+closures_offsets_arity([], _) ->
+ [];
+closures_offsets_arity(ExposedClosures, SDescs) ->
+ Offsets = [Offset || {_, Offset, _} <- SDescs],
+ %% Offsets and closures must be sorted in order for find_offsets/3 to work
+ SortedOffsets = lists:sort(Offsets),
+ SortedExposedClosures = lists:keysort(1, ExposedClosures),
+ find_offsets(SortedExposedClosures, SortedOffsets, []).
+
+find_offsets([], _, Acc) -> Acc;
+find_offsets([{Off,Arity}|Rest], Offsets, Acc) ->
+ [I | RestOffsets] = lists:dropwhile(fun (Y) -> Y<Off end, Offsets),
+ find_offsets(Rest, RestOffsets, [{I, Arity}|Acc]).
+
+%% The functions below correct the arity of calls, that are identified
+%% by offset, in the stack descriptors.
+fix_sdescs([], SDescs) -> SDescs;
+fix_sdescs([{Offset, Arity} | Rest], SDescs) ->
+ case lists:keyfind(Offset, 2, SDescs) of
+ false ->
+ fix_sdescs(Rest, SDescs);
+ {?SDESC, Offset, SDesc} ->
+ {ExnHandler, FrameSize, StkArity, Roots} = SDesc,
+ DecRoot = fun(X) -> X-Arity end,
+ NewRootsList = lists:map(DecRoot, tuple_to_list(Roots)),
+ NewSDesc =
+ case length(NewRootsList) > 0 andalso hd(NewRootsList) >= 0 of
+ true ->
+ {?SDESC, Offset, {ExnHandler, FrameSize-Arity, StkArity,
+ list_to_tuple(NewRootsList)}};
+ false ->
+ {?SDESC, Offset, {ExnHandler, FrameSize, StkArity, Roots}}
+ end,
+ RestSDescs = lists:keydelete(Offset, 2, SDescs),
+ fix_sdescs(Rest, [NewSDesc | RestSDescs])
+ end.
+
+
+%%------------------------------------------------------------------------------
+%% Miscellaneous functions
+%%------------------------------------------------------------------------------
+
+%% @doc A function that opens a file as binary. The function takes as argument
+%% the name of the file and returns an Erlang binary.
+-spec open_object_file(string()) -> binary().
+open_object_file(ObjFile) ->
+ case file:read_file(ObjFile) of
+ {ok, Binary} ->
+ Binary;
+ {error, Reason} ->
+ exit({?MODULE, open_file, Reason})
+ end.
+
+remove_temp_folder(Dir, Options) ->
+ case proplists:get_bool(llvm_save_temps, Options) of
+ true -> ok;
+ false -> spawn(fun () -> "" = os:cmd("rm -rf " ++ Dir) end), ok
+ end.
+
+unique_id(FunName, Arity) ->
+ integer_to_list(erlang:phash2({FunName, Arity, now()})).
+
+unique_folder(FunName, Arity, Options) ->
+ DirName = "llvm_" ++ unique_id(FunName, Arity) ++ "/",
+ Dir =
+ case proplists:get_bool(llvm_save_temps, Options) of
+ true -> %% Store folder in current directory
+ DirName;
+ false -> %% Temporarily store folder in tempfs (/dev/shm/)
+ "/dev/shm/" ++ DirName
+ end,
+ %% Make sure it does not exist
+ case dir_exists(Dir) of
+ true -> %% Dir already exists! Generate again.
+ unique_folder(FunName, Arity, Options);
+ false ->
+ Dir
+ end.
+
+%% @doc Function that checks that a given Filename is an existing Directory
+%% Name (from http://rosettacode.org/wiki/Ensure_that_a_file_exists#Erlang)
+dir_exists(Filename) ->
+ {Flag, Info} = file:read_file_info(Filename),
+ (Flag =:= ok) andalso (element(3, Info) =:= directory).
+
+%% @doc Function that takes as arguments a list of integers and a list with
+%% numbers indicating how many items should each tuple have and splits
+%% the original list to a list of lists of integers (with the specified
+%% number of elements), i.e. [ [...], [...] ].
+-spec split_list([integer()], [integer()]) -> [ [integer()] ].
+split_list(List, ElemsPerTuple) ->
+ split_list(List, ElemsPerTuple, []).
+
+-spec split_list([integer()], [integer()], [ [integer()] ]) -> [ [integer()] ].
+split_list([], [], Acc) ->
+ lists:reverse(Acc);
+split_list(List, [NumOfElems | MoreNums], Acc) ->
+ {L1, L2} = lists:split(NumOfElems, List),
+ split_list(L2, MoreNums, [ L1 | Acc]).